Spektrum 2.4 4.8v RX battery?

[Kim Taylor]

I've now noticed an unfortunate typo in my above post, which I can't edit - maybe a mod can correct it for me😚

Kim 

[GaryW]

38 minutes ago, Nigel R said:

 

how many servos does it use on loaded flight controls? It only has rudder/elevator IIRC.

 

Its fitted with 4 Hitec HS645MG's Nigel..... Throttle, Rubber & 2 on the Elevators,,,, The plane is as the previous owner built it & set it up including the Rx Batts... and they are in balance with each other in voltage which i check every time I charge them so ne need for a sub c or lipo pack ,, Also I'm of the persuasion & mind set of " If it aint broke don't fix it "

Edited August 5 by GaryW

[RottenRow]

38 minutes ago, Kim Taylor said:

What I now suspect is that my charger sensed a false peak and shut off well before the pack was fully charged. On reflection at the time, alarm bells should have rung as the charging time was unusually short.

 

Good point... I think this happens a lot, many probably get away with it by luck rather than anything else, as their battery probably still contained sufficient charge from previous uses.

 

I never use a delta peak charger to charge my NiMHs unless on the rare occasion I want to top one up at the field. Otherwise I always charge at 0.1C for 14 hours plus (ie the old fashioned way). Usually the night before flying.

 

As a check, I occasionally discharge the packs using a cycler (my old SM Services units all still work fine) and this will point out the gradual decline in cell capacity over time.

 

You've not derailed the discussion and if someone learns something from it, it will have been worthwhile.

 

Brian.

[Nigel R]

Well, maybe I can't convince you Gary... but, checking the voltage is the same doesn't avoid the problem of nimhs simply not being electrically suitable for parallel connection. There does appear to be an amount of misinformation out there, unfortunately. Ultimately - you want more current, fit a different cell type, if you want redundancy, fit a failover device. Another route to putting some redundancy in there (and this is cheap and easy to arrange BTW 🙂 ) would be splitting the batteries across the servos, e.g. one battery runs a single elevator plus the throttle, and the other powers rudder and elevator, for instance. To improve this further you could run the RX from both batteries through diodes, which gives the RX true redundancy. The RX draws very little current and this is a really, really simply method of failover (but not ideal for high current, e.g. servos)

 

As to current capability, I think a single AA pack would be ample for the three 645s on the controls on this model. The worst case - but still recoverable - scenario I can think of here is where you have one stalled elevator; the 645 stall current is 2.5A, and one single AA eneloop pack can put out well beyond 2.5A for an extended period of time, i.e. you're well within capability to get the model back down (assuming you can still do so with one bust elevator).

 

 

Edited August 5 by Nigel R

[Nigel R]

9 minutes ago, RottenRow said:

I never use a delta peak charger to charge my NiMHs unless on the rare occasion I want to top one up at the field. Otherwise I always charge at 0.1C for 14 hours plus (ie the old fashioned way). Usually the night before flying.

 

As a check, I occasionally discharge the packs using a cycler (my old SM Services units all still work fine) and this will point out the gradual decline in cell capacity over time.

 

Snap.

 

A trickle charge of nimh packs will also perform the task of ensuring they are balanced.

 

Trickle charge is very low tech, but it works rather well for nimh.

[GaryW]

18 minutes ago, Nigel R said:

and one single AA eneloop pack can put out well beyond 2.5A for an extended period of time, i.e. you're well within capability to get the model back down (assuming you can still do so with one bust elevator).

 

 

 

Actually both Rx packs are infact eneloop packs ,,, Must have forgotten to mention that in my earlier post Nigel.... And it's not that a I can't be convinced more along the lines of all the time its working fine leave well alone but is anytime I notice an issue then I wud normally look to a solution    On another note ,, whatever all this misinformation is out there,,, I wudn't know I've never read it as I find reading boring as hell.....

 

 

Edited August 5 by GaryW

[Peter Christy]

15 minutes ago, Nigel R said:

 

Snap.

 

A trickle charge of nimh packs will also perform the task of ensuring they are balanced.

 

Trickle charge is very low tech, but it works rather well for nimh.

Trickle charging NiMHs (or NiCADS) is OK occasionally, but not something to do regularly. It will inevitably lead to the cells being over-charged, venting gas and drying out the electrolyte inside. This is not good!

 

It was the introduction of peak-detect chargers that led to the virtual disappearance of "black wire corrosion", which was primarily caused by the cells venting caustic gas when trickle charged regularly.

 

I normally discharge my packs after the winter layoff and give them a trickle charge to balance them. I then do a capacity check on them, and thereafter just peak detect charge them until the following winter.

 

Most modern chargers will display how much charge the cells have taken, and as long as this is in line with their use since the last charge, then you should be good to go.

 

--

Pete

 

[FlyinFlynn]

1 hour ago, Peter Christy said:

It will inevitably lead to the cells being over-charged, venting gas and drying out the electrolyte inside.

Not sure I agree with this Peter. Providing you are not keeping the cells on trickle charge more than the recommended 12 to 14 hours at or below the 0.1C rate IMHO there is no chance of the nimh being sufficiently overcharged to cause gassing. There is a far greater risk in overcharging cells by fast charging than trickle charging and it is doubtful fast charging will allow sufficient time to get the pack properly balanced.

 

Also not too sure about your claimed cause for black wire corrosion too, I have never seen any definitive evidence as to the direct cause of black wire corrosion, can anybody point me in the right direction on that?   There is plenty of anecdotal evidence though!  Was it the development of fast peak detect chargers that saw the reduction of black wire corrosion or was it a change in the composition of the wires and the sheathing (for example).

/2p

[Nigel R]

2 hours ago, Peter Christy said:

Trickle charging NiMHs (or NiCADS) is OK occasionally, but not something to do regularly.

 

I'd respectfully disagree, too. Trickle charge does not overcharge cells - when they are full the response moves over to a temperature rise in the cell. The cell is also dissipating heat all the time. 

 

At a very low current, say 100mA, each cell is only having to deal with about 0.15 of a watt of heat.

[Phil Green]

Well, I agree with Pete in principle but as ever 'it depends' 🙂  

I tend to go with industry recommendations and datasheets as its an unfortunate fact that NiMh is not as tolerant of overcharging as NiCd was.
A simple trickle charger is just a high voltage with a current limiter - if left connected this will continue to feed current into the battery long after its fully charged, in its attempt to raise the battery to its own output voltage (which is way above a safe voltage for the battery).   
All of the NiMh cell manufacturers datasheets that I could find recommend peak detect.

At 0.1C an overnight trickle-charge is probably ok, but 10 hours at 0.1C is a full charge, and if say the pack began at 50% SoC,  internal losses will convert five hours of overcharge into five sustained hours of heat which is bad for NiMh and can ultimately lead to venting or rupture. 
Ideally the charge should stop when the pack is full, there is no advantage in continuing the charge beyond that.
We had one bloke in the SSA who used to leave his batteries permanently on a 0.1C trickle between flying sessions which is both extreme and very bad practise! 🙂  
And of course if trickle charging at a higher rate, say 0.2 to 0.3C then you have to be even more cautious - at least have a capacity cut-off.
If asked I would always suggest following the cell manufacturers instructions (the actual manufacturer, not the reseller). They rarely, if ever, recommend trickle-charging 🙂

 

[Peter Christy]

Thanks to Phil for a very clear explanation!

 

To amplify my comments on venting and "black wire corrosion": The vents on a pen-cell (or similar) are at the positive end of the cell. The vented gas has a slight, but noticeable, positive charge. This attracts it to the negative end of the battery. The gas itself is relatively harmless - to the battery, anyway. The problem arises if the air is at all damp, which it frequently is in the UK. When the gas is absorbed into water, you end up with a very caustic solution, which will eat away the wiring quite quickly.

 

This is why black wire corrosion was most common during the wet winter months, charging in damp sheds, garages, etc. Those who kept and charged their models in the house seemed to suffer from it less. It actually didn't matter what colour the wire was, either. Its just that black was the traditional colour for negative leads.

 

This was all explained to me decades ago by the representative of one of the battery companies at the height of the black wire corrosion scare.

 

The problem has all but disappeared since peak detect chargers became common place.

 

Trickle charging still has its place, as it does balance the cells. However, I stand by my point that it is not something to do on a regular basis.

[Cuban8]

Black wire corrosion.....oh dear, a minefield if ever there was one and even with an explanation from what might be considered an expert source as Pete suggests, I still don't believe we've really ever got to the bottom of it IMHO.

 

I never, ever, rapid (peak) charge my nimhs in TX and RX - I don't like the way that nimhs that have been rapid charged on the field by club mates always show a fairly significant temperature rise which to me suggests that the cells are under stress. I do have a decent smart rapid charger for domestic batteries used round the house in various appliances, and it always makes them too hot.

 

A regular, simple and straightforward capacity check with an ordinary four button charger will  keep an eye on batteries and will flag up a possible problem long before any risk of failure leading to a crash becomes significant. This is pertinent whether you peak detect or trickle charge.

 

Just a few points about how I go about things that have worked for me for many years, I'm sure others may go about thing differently as there are so many grey areas associated with this subject.

[Nigel R]

21 hours ago, Phil Green said:

internal losses will convert five hours of overcharge into five sustained hours of heat which is bad for NiMh and can ultimately lead to venting or rupture. 

 

How much heat though?

 

0.1C (or 200mA), with a 1.5V terminal voltage (ish), that's 0.3W in each cell. Whilst I don't know the maths to work out what temperature rise that would cause in a nimh, a solid block of aluminium the size of an AA cell would be raised 40degC over 12 hours (says the first online calculator I found) which is significant.

 

But

 

Nicads used to trickle at about 50mA IIRC which is why I suspect is the main reason they were just fine with any trickle charging use and abuse - the physical size is the same as nimh of course, but they were only asked to deal 0.075W of heat when full.

[Mike Blandford]

The heating of NiCd and NiMh batteries while charging is confused by the fact that the chemical reaction of NiCd while charging is endothermic (cools down) while that for NiMh is exothermic (heats up). Both will, of course, heat up once fully charged if a charging current is still present.

 

Mike

[Nigel R]

Is the temperature change due to these reactions significant Mike?